In 2009, the United States Marine Corps selected the M27 Infantry Automatic Rifle to partially replace the M249 in USMC service.

[8] The M60 was a more mobile general-purpose machine gun intended to be carried by troops to provide heavy automatic fire.

)[11] "Designated riflemen" in every squad were ordered to use their weapons on the fully automatic setting, while other troops were required to use their rifle's semi-automatic mode on most occasions to increase accuracy and conserve ammunition.

[8] The Army decided that an individual machine gun, lighter than the M60, but with more firepower than the M16, would be advantageous; troops would no longer have to rely on rifles for automatic fire.

[15][16] The Stoner 63 LMG saw combat for a brief period in Vietnam with the Marine Corps, and later on a wider scale with the U.S. Navy SEALs.

[21] Prior to July 1972, SAW development contracts were awarded to Maremont, Philco Ford, and the Rodman Laboratory at Rock Island Arsenal, which produced the XM233, XM234, and XM235, respectively.

Opinions on the 6 mm cartridge were mixed due to the logistical implications of having multiple calibers in infantry service.

[28] In May 1980, the FN XM249 was selected as the best choice for future development on the grounds of performance and cost, while the HK XM262 reportedly came a close second.

[28] In September, FN was awarded a "maturity phase" contract for further development of the XM249,[29] and testing of the new weapon began in June 1981.

[34] Although found to be reliable and accurate, multiple safety hazards were identified in the design, including sharp edges and an exposed hot barrel.

[37] It was praised for its extreme durability and massive firepower, but was criticized for a number of issues: the blank firing adapter fitted poorly, the bipod was fragile, the sling attachment was awkward, and there were many slots and gaps that accumulated dirt.

[45] The standard squad automatic weapon in Afghanistan was the M249 with PIP kit, which served alongside its heavier counterpart, the M240 machine gun.

Most M249s were given a collapsible buttstock immediately prior to the invasion to reduce its length and make the weapons more practical for parachuting and close-quarters combat.

[2] A report entitled Lessons Learned in Afghanistan was released by Lieutenant Colonel Charlie Dean and SFC Sam Newland of the U.S. Army Natick Soldier Center in 2002.

[45] The lethality of the 5.56 mm ammunition has been called into question by reports of enemy soldiers still firing after being hit multiple times.

[45] Operation Iraqi Freedom PEO Soldier Lessons Learned, a report on the performance of weapons in the Iraq War, was published by Lieutenant Colonel Jim Smith of the U.S. Army in May 2003.

He praised the SPW variant, noting that its "short barrel and forward pistol grip allowed for very effective use of the SAW in urban terrain".

He said that a cloth pouch was preferred over the plastic box for holding linked ammunition, and that "knock-down power is poor, but is compensated by rate of fire".

M249 users had the lowest levels of satisfaction with weapon maintainability at 70 percent (239 troops), most due to the difficulty in removing and receiving small components and poor corrosion resistance.

[51][52] With plans to buy up to 4,100 IARs to complement and partially replace its 10,000 M249s, of which 8,000 will remain in service, held at platoon level,[53] it acquired 450 of the Heckler & Koch HK416–based weapons for testing.

[7] The Marines started fielding the M27 in 2010, but kept both weapons in the inventory due to the M249's greater ammunition capacity and higher sustained fire rate.

[54] The Army passed on the concept of the IAR, believing automatic rifle with a magazine would lower the effectiveness and firepower of a squad.

Belts are typically held in a hard plastic or soft canvas box attached to the underside of the weapon.

This pressure moves a piston providing the energy to extract and eject the spent casing as well as advance the belt and compress the recoil spring, thus preparing for subsequent shots.

[61] In addition, the dual gas port settings were reduced to only one; M249s with the product improvement kit can no longer fire at a higher cyclic speed.

[62] Over the years, additional modifications have been introduced as part of the Soldier Enhancement Program and Rapid Fielding Initiative.

These include an improved bipod, 100– and 200–round fabric "soft pouches" (to replace the original plastic ammunition boxes), and Picatinny rails for the feed tray cover and forearm so that optics and other accessories may be added.

[46][63] An extensive maintenance program intended to extend the service life of M249 SAWs has been carried out, especially units that suffered from wear due to heavy use.

The SPW's lightweight barrel is longer than that of the Para model, giving it a total length of 908 mm (36 in) and a weight of 5.7 kg (13 lb).

A request was put in for a new machine gun in 2001, and FN responded with a scaled-up version of the M249 SAW weighing in at 18.5 lb (8.4 kg) with an overall length of 39.5 in (100 cm).